This multi-center protocol will test the hypothesis that intervention during the prodromal period of IDDM will delay its clinical onset. The protocol developed from studies in diabetes-prone animals which showed that parenteral and oral insulin treatment delayed the onset of IDDM. Primary endpoints are preservation of islet cell function measured by C-peptide or insulin response to oral glucose or in an ivGTT measured at 6 month intervals, with immunity to islet cell antigens as secondary endpoints.